U.S. Pat. No. 4,543,966 and UK patent No. 2,099,703 relate to a bone marrow biopsy needle assembly which comprises an elongate hollow needle having open front and rear ends, the front end being provided with a cutting edge: furthermore, a portion of the needle, adjacent its front end, is of a reduced internal diameter and an internal shoulder is formed between the inner end of this reduced-diameter portion and the WIDER main portion of the needle. The hollow needle is used with a trocar needle or stilette which is inserted into the hollow needle from its rear end, for a pointed front end of the trocar needle to project beyond the front end of the hollow needle.
In use, this assembly is gradually advanced, by hand, through the soft skin tissue and then through the cortical bone of the patient, by the execution of alternate clockwise and counterclockwise rotations of the assembly around its longitudinal axis. Once the assembly has advanced through the cortical bone, to reach the underlying spongy or medullary bone, the trocar needle or stilette is withdrawn from the hollow needle: then the hollow needle is advanced into the spongy bone, again by the execution of alternate clockwise and counterclockwise rotations or rotary motions of the hollow needle; it will be appreciated that a core sample of bone marrow will accordingly enter the hollow needle, from its front end. When the hollow needle has been advanced to a sufficient depth into the spongy bone, about 20 to 25 mm, the hollow needle is rotated several times about its longitudinal axis to sever all the trabecular connections at its base and break the core sample loose from the rest of the spongy bone, and is then withdrawn. The core sample of bone marrow is retained within the hollow needle and this retention is particularly facilitated by the internal step which acts as a shoulder and also because of the fact that the core sample expands in diameter in the wider portion of the needle, inwardly or to the rear of the front end portion of reduced internal diameter. The core sample is subsequently removed from the hollow needle by inserting an elongate pusher rod into the hollow needle from its front end.
The above-described biopsy needle assembly is effective in use but it is necessary to make the hollow needle by hand, in order to provide its front end portion of reduced diameter: the hollow needle is accordingly expensive to manufacture. Also, I have now devised a modification to the needle in order to improve its ability to advance through the cortical bone.